Process for making zirconium alloys



nited States The present application is a continuation-in-part of patentapplication Serial No. 33,907, filed June 6, 1960, by the sameapplicants, and now abandoned.

This invention relates to alloys suitable, inter alia, f r use at hightemperatures in an atmosphere of carbon dioxide.

Consideration has been given to the use of alloys of zirconium asstructural materials within the cores of graphite-moderated carbondioxide-cooled nuclear reactors.

Alloys of zirconium with copper and/ or chromium and molybdenum havingadequate resistance to creep and with good corrosion resistance up totemperatures of the order of 525 C. have been developed as described inUS. Patent No. 2,924,518, filed by us on July 17, 1958, and assigned toMetropolitan-Vickers Electrical Co. Ltd.

It has now been discovered that if tungsten is added to azirconium-copper alloy, the corrosion resistance properties are furtherenhanced.

An alloy according to the invention consists of from 0.5% to 1.5%, byweight, of copper, from 0.25% to 1.5% by weight of tungsten with theremainder zirconium, except for impurities as may be unavoidablypresent. Such impurities may arise from their inclusion in spongezirconium from which the zirconium content of the alloy is derived.

Examples of preferred alloys within the range of constituents covered bythe invention are as follows:

(a) Copper 0.5%, tungsten 0.5 remainder zirconium. (b) Copper 1.5%,tungsten 1.0%, remainder zirconium.

The resistance to corrosion by carbon dioxide of alloys given by theabove examples may be judged by the gain in weight of the alloy when incontact with carbon dioxide for an extended period at an elevatedtemperature. Weight gain of the alloys exemplified, compared with theweight gains under the same conditions of zirconium, the alloy known asZircaloy-Z and consisting of 13-16% tin, 0.07- 0.2% iron, 0.050.l%chromium and 0.030.08% nickel; an alloy of zirconium with 0.5% copperand 0.5% molybdenum, and an alloy of Zirconium with 1.0% copper and 1.5%molybdenum are given in the following table:

Exposure to C 0 at atmospheric pressure and 700 C.

If this exposure is increased to 1200 hours, the gain in weight of alloy(a) increases to 11.5 mg./cm. while the gain in Weight for the alloycontaining 0.5 copper and 0.5 molybdenum increases to 25 mg./cm. In thesame conditions, the gain in weight for alloy (b) is only 7.6 mg./cm.

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The alloys (a) and (b) have thus appreciably higher corrosion resistancein CO than the zirconium-coppermolybdenum alloys, and alloy (b) has evensuperior resistance to alloy (a). Both alloys (a) and (b) have a muchgreater resistance to corrosion than Zircaloy-2.

For the zirconium-copper-tungsten alloys of the invention to exhibit theenhanced corrosion resistance desired, it is essential for the alloys tobe homogenous and threephase. In the event that the tungsten ispermitted, during production, to segregate in the zirconium, and thismay happen as a result of the widely difiering melting temperature ofzirconium ('1600 C.) and tungsten (300O C.), corrosion may well occur atthose parts of the alloy where the segregated tungsten is exposed to theaction of heated carbon dioxide with the resulting formation ofolive-greencoloured oxide blisters.

In order to obtain the required ternary alloy of the invention, it isessential to proceed in the following manner. An alloy of tungsten andcopper containing approximately equal proportions, by weight, is firstprepared by compacting an intimate mixture of powdered copper andpowdered tungsten, and then sintering the mixture. The proportions ofthe mixture may be varied when it is desired that the final alloycontains other than equal proportions of the alloying ingredients. Thesintered alloy is then melted in a non-consumable electrode argon arcfurnace by heating to a temperature between 1200 C. and 1600 C. withzirconium to give a master alloy containing approximately 18% copper,and 18% tungsten, by weight. This master alloy is again melted and thendiluted by the addition of further amounts of zirconium to make thealloys in the required range. The resultant alloys are homogeneous andthree-phase.

By the multiple melting process above described, the coppertungstenmaster alloy initially produced is progressively diluted with thezirconium, and the segregation of the tungsten thereby avoided.

What we claim is:

The process of manufacturing a ternary alloy of zirconium with from 0.5to 1.5%, by Weight, of copper, and from 0.25% to 1.5%, by weight, oftungsten, which comprises intimately mixing substantially equalproportions, by Weight, of powdered copper and powdered tungsten,sintering said mixture, melting said sintered mixture and addingzirconium to form a master alloy of copper, tungsten and zirconium, andmelting a required proportion of said master alloy with additionalzirconium in order to obtain a homogeneous ternary alloy.

References Cited by the Examiner UNITED STATES PATENTS 2,030,229 2/1936Schwarzkoff 177 X 2,813,073 11/1957 Saller et a1 75177 X 2,924,5182/1960 Raine et al. 75-177 2,932,887 4/1960 McCuaig et al. 75l77 XFOREIGN PATENTS 488,322 7/ 1938 Great Britain.

OTHER REFERENCES AECU 3561, Scaling of Zirconium and Zirconium Alloys,US. Atomic Energy Comm, August 1957 (page 12 relied upon).

DAVID L. RECK, Primary Examiner.

WINSTON A. DOUGLAS, Examiner.

